These documents contain no rigorous scientific evidence, but refer to it, and the FBI explains its rationale for accusing Ivins in overviews scattered through the documents.

The argument boils down to the anthrax being specifically traced to a spore-containing flask of which Ivins was the master. Called RMR-1029, it was also referred to by Ivins as "Dugway Ames spores - 1997," apparently from its original point of manufacture, at Dugway Proving Ground in Utah, an Army biodefense center administered by a company called Battelle.

The source sample

RMR-1029 was genetically typed by the FBI through an independent company, and uniquely linked to the mailed anthrax in 2004-2005. However, part of the investigation was engaged in building a repository of Ames strain anthrax isolates from every laboratory in the United States in possession of samples. As part of the inventory, Ft. Detrick had to derive specific unique characteristics for all of its sources of Ames. Genetic testing allowed the FBI to distinguish special mutations unique to all isolates so as to be able to compare them with the signature derived from the anthrax mailings.

The FBI states in its documents that Ivins furnished two sets of samples in February of 2002 in complying with this part of the investigation, representing them as drawn from RMR-1029. This set was unusable, explains the FBI, at which point Ivins was asked to furnish a second set. Given to the FBI in April 2002, these samples did not genetically match the mailed anthrax.

In December of 2003, an FBI agent again surveyed the lab where RMR-1209 resided, identifying cultures of Ames which had not been submitted in the initial part of the investigation. Four months later Ivins furnished culture slants taken from these sources to the FBI. On the same day (although the statements are a bit unclear), the FBI returned to the lab and seized the original samples, as well as RMR-1029, which was eventually removed to the Navy Medical Research Center. When the seized RMR-1029 was tested, its genetic mutation profile matched with the mailed anthrax.